This post is in a sense a twin of my last post. That post grew out of some featured articles on Autonomous Vehicles in a recent issue of "Science" magazine (see http://sigma5.blogspot.com/2018/01/robot-cars-now-new-and-improved.html for details). This post grows out of an item in the "Books" section of the same issue. The subject is Arthur C. Clarke. The occasion is a celebration of the fact that December 15, 2017 was the hundredth anniversary of his birth.
So who was Arthur C. Clarke and why does he deserve to have his centennial celebrated? He can best be described as a "futurist". Since he did most of his work before the word had been invented he went about it in the then usual way, he wrote Science Fiction. But like his contemporary Isaac Asimov he also wrote a considerable amount of nonfiction.
The article suggests rereading two of Clarke's works. Since I had both on my bookshelf I proceeded to do just that. They recommended "The Exploration of Space" as a nonfiction selection and "Childhood's End" as a fiction selection. They were both good choices. Before getting into them let me review his life focusing on his technical (i.e. factual) achievements. I will then move on to the two specific books and rope in some his other fictional work.
Clarke was born in the U. K. and died ninety years later in Sri Lanka after living there for many years with his "partner". Being openly gay was just not done at that time but he did not make a serious effort to hide his sexual orientation. He was always interested in technical subjects especially rockets and space flight. His first brush with cutting edge technology happened during World War II. He spent most of the war working on a classified project to provide ground assist to airplanes attempting to land in fog. This was a big problem during the war. The project didn't pan out at the time but influenced subsequent events.
Shortly after the war he introduced the world to geosynchronous satellites. The International Space Station (ISS) orbits near the earth about once every 90 minutes. The moon orbits much further out with a complete circle taking 28 days. It stands to reason that somewhere in between a satellite can take exactly 24 hours to orbit. And if it orbits in the correct direction over the equator it will appear to be completely stationary in the sky when viewed from the surface of the Earth.
Clarke published details of this in the October 1945 issue of "Wireless World". Therein he gave the proper altitude (about 22,000 miles) and the fact that three satellites poised 120 degrees apart would provide complete coverage. He also provided many other details, technical and otherwise. This was all more than a decade before the Russians launched Sputnik, the first man made satellite.
In 1979 he introduced the idea of a space elevator to the public in a science fiction book called "The Fountains of Paradise". Again, the idea is simple. If you could stretch a wire from the surface of the Earth to a point far out in space you could then attach an elevator to it. If you also hooked up electric power lines that the elevator could use then you would have an extremely efficient way to move things to and from space.
There are many technical problems. No material exists that is strong enough to be used for the wire. And that's just the beginning of the list of potential difficulties. But if a working space elevator could be built and turned out to be practical to operate it would completely revolutionize space travel.
And with that let me turn from nonfiction to fiction. (I will get back to nonfiction later.) "Childhood's End" is a great example of the creativity Clarke displayed during his entire life. The book was released in 1953, again before a single man had traveled into space. I recommend the book. But I can also recommend the 3 part miniseries of the same name that the SyFy channel broadcast in 2015 to those who don't want to hunt up a copy of the book. If you aren't already familiar with the story then the next part contains spoilers.
***** Spoiler alert.
In the book (the plot of the miniseries differs slightly but retains the important plot points) humanity is on the verge of sending men into space. All of a sudden giant space craft appear all over the earth. The "Overlords" announce their presence and decree that mankind will be deprived of space travel. Otherwise they are benign and helpful. But for reasons not explained at the time they refuse to reveal themselves. With the beneficial guidance of the Overlords war is abolished and material progress advances quickly. Earth becomes a paradise.
This goes on for some time. Finally, the Overlords reveal themselves. They look like classical devils out of mythology with horns and tails. But by this time humanity has been so accustomed to them and their reputation for benevolence is by now so well established that they are accepted with little trouble. Material progress continues but other kinds of progress comes to a nearly complete halt. First class art and significant scientific progress now seems somehow beyond the ability of current generations of humanity. Some people are concerned about this but most are not. No substantial opposition to the Overlords materializes.
We now reach the final stage. One day all the children below a certain age start changing drastically. The become literally superhuman. They attain superpowers and eventually all leave Earth for some unknown destination. Left behind are everyone above the cutoff age including the children's parents. Those humans left behind are now all sterile. There will be no more children and the non-evolved type of humanity will die off in a generation. "For humanity childhood has ended". Finally we learn that this is a transition that is common in the universe. And for some reason the Overlord race can't make it. They are doomed to be perennial midwives. So in the end we find out they are tragic figures.
***** End spoiler section
This was serious stuff. It was not at all the "ray guns, babes, and big headed aliens" that is the stereotypical Science Fiction fodder of the period. Clarke was great at coming up with creative and original thinking. He was not so good at characterization. Late in his career he wrote the "Rama" series. This was a serious but fictional take on what it would actually be like if an alien space ship took a swing through the solar system and chose not to stop. The books were very popular because of the seriousness with which they treated their subject and because of the care Clarke took with technical details. But they are a slow read.
Let's return to Clarke's nonfiction work. "The Exploration of Space" was written in 1951. I have the updated version that came out in 1959. The changes are fairly modest. By 1959 Sputnik had been launched but the Russian "Luna" mission, the first time the far side (often erroneously referred to as the "dark" side in the pre-Luna era) of the moon had been photographed, had not yet happened. It was also before Gagarin, the first man in space had taken his rocket ride in 1961. So Clarke sprinkled the results from these early space shots into the text but that left it little changed.
The book can be divided into two parts. The early sections are "rocket science for regular people". Unlike today, Clarke correctly assumed that readers of the time could handle some simple mathematics. (Modern writers are justifiably afraid of doing this because of the current widespread fear of actual facts.) He does a nice job of covering the basics.
The most important tenet of rocket science is "it's all about delta-v". "V" for velocity is speed and direction combined. And "delta" is tech talk for "change in". So a change in speed counts as delta-v. But a change in direction (or a combination of the two) does too. When it comes to using a rocket to get from here to there the key thing to figure out is how much delta-v you need. To get from the surface of the earth to LEO (Low Earth Orbit) you need a delta-v of 17,000 MPH (miles per hour). To completely break free of Earth's gravitational field you need another 8,000 for a total of 25,000 MPH. In practical terms, getting to LEO gets you most of the way to practically anywhere.
Clarke does a nice job of laying all this out. He works through several examples like getting from LEO to the Moon or LEO to Mars or LEO to Venus. This is enough examples to show what's involved in getting from pretty much anywhere to pretty much anywhere else. And the delta-v required to get from LEO to the Moon or Mars or Venus (or pretty much anywhere else) is far less than 17,000 MPH. He also provides a basic tutorial on how rockets work and what can be done with a "chemical" rocket, a rocket powered by the traditional method of burning stuff.
Chemical rockets just don't work that well. It is possible to make one that can produce a delta-v of 25,000 MPH but it means the rocket consists almost entirely of fuel. There are some tricks like multiple stages that help. But none of the tricks work well enough to substantially improve the situation. This failure is one reason people are so interested in space elevators, for instance. Clarke does not investigate space elevators in this book but he does investigate alternatives like atomic powered rockets. He does not delve very deeply, however.
In the second part of the book he goes into how we would do this or that. Given that he is doing this before we had any practical experience with space travel he does a remarkably good job. For instance, he talks about various practical aspects of space travel. He calculates roughly how many pounds per day an astronaut would need to survive in space. At the time a "man in the can" was a given because no practical alternative yet existed.
The technology of the '50s was obviously not up to the task in several areas so he was forced to speculate. But pretty much every technical advance he foresees did not come to be. This leads him to conclude that certain missions that are beyond even our current capability would be feasible. In other areas he completely misses technical advances that redefined what was possible. It turns out that predicting the future is really hard to do.
Most obviously he missed the development of small, powerful, resource stingy, computers and other electronic devices of astonishing capability. This has allowed the "man" in the can to be replaced by electronics. The savings have made it possible to send robot missions to Mercury, Pluto, and many of the places in between. These missions are literally impossible to do if people have to come along for the ride.
He also spends some time on large telescopes. He correctly identifies the two big limitations at the time on telescope design but finds no solutions to either. The first was weight. As you make the mirror bigger it must be more and more rigid so that it doesn't distort due to the influence of gravity. The practical limit had already been achieved by the 200" Palomar telescope. A substantially bigger mirror would distort to the point where the image would be inferior to what the Palomar mirror was capable of.
The other problem is caused by the fact that the atmosphere is always in motion. That means that when you look at some object in space small moving lumps of air between the object and the telescope act like lenses and bend light. At some point "atmospheric distortion", even on the best of nights, again degrades the image. And again the Palomar telescope is about as big as you could go before atmospheric distortion results in a poorer image from the larger mirror.
Both of these problems were eventually solved and Clarke saw neither solution coming. Large mirrors are now made of segments. Each segment is smaller than the 200" Palomar mirror and sophisticated machinery makes sure that each segment has the right shape and is pointed correctly. The diameter of the Palomar mirror is 5 meters. A 5 Meter telescope mirror is now considered to be on the small side.
The solution to the atmospheric distortion problem is adaptive optics. The mirror surface is literally bent and twisted many times a second to cancel out the atmospheric distortion. And powerful computer processing also allows two telescopes to operate as if they were a single telescope whose mirror diameter is the distance between them. Earth based telescopes are literally capable of feats unimaginable to Clarke. His solution was to put telescopes in space or on the moon. Space based telescopes (Hubble now, and soon the James Webb Space Telescope) do exist but only in small numbers. No one has tried to put a telescope on the moon.
I'm not trying to knock Clarke here. What I am actually saying is that the prediction business is extremely difficult to do. He does it as well as anybody can. But the results are off the mark for the most part. Let me digress into fiction for a moment before finishing up with some more fact.
Clarke wrote a short story called "The Sentinel". At some point it attracted the attention of a movie director named Stanley Kubrick. The resulting collaboration produced "2001: A Space Odyssey". If you are not familiar with it and you check it out your reaction will probably be "what's the big deal?" But "2001" was a breakthrough and became hugely influential. And so many of the things that made it special at the time have been incorporated into out culture to such an extent that they are no longer noteworthy. And it turns out that "2001" incorporated many of the key aspects of "Childhood's End". So let me review some key plot points.
The movie revolves around the influence of a "monolith". This is a dark rectangular object whos dimensions are in the ratio of 1x4x9 (one then two squared then three squared). We first see some apes fooling around with a monolith in the background. The apes discover weapons. One ape throws a bone into the sky and it morphs into a satellite. This is one of the all time great transitions in movie history. We next follow a scientist who is sent to investigate an "anomaly" on the moon, another monolith. This monolith sends a signal that causes a mission to Jupiter to be undertaken.
For the most part the space ship was operated by the now infamous HAL computer. HAL goes nuts and kills all the astronauts but one. The surviving astronaut gets to Jupiter where he encounters another monolith. There the monolith puts him through what can only be described as a psychedelic experience. This transforms the astronaut into the "Space baby" that the movie ends with.
In "The Sentinel" an object is found on the moon. An attempt is made to take a sample. The object is impervious. You can't hammer a chunk off of it. you can't scratch it with a diamond. You can't melt it with a blow torch. Finally a nuclear weapon does the job. The idea is that the object is sending a "heartbeat" signal to some unknown destination. When the object is destroyed the signal stops and some unknown race learns that there is now a space faring civilization on Earth.
"2001" combines this idea with that of the Overlords. In 2001 they are no longer devils. Now they are mysterious monoliths. But the idea is the same. They transform apes into humans and they transform humans into star children. This is the core evolutionary path in "Childhood's End". With Kubrick's help the story is told in a much more compelling way than it was in Clarke's book. But at it's core it is the same story. And it is a very interesting and imaginative story.
Back to fact. You would think that the science of rocketry would have advanced from the '50s when Clarke was writing "Exploration" to now. But that turns out to not be true. I have covered the state of the art of rocketry in several posts. Here's a link to my first post on the subject: http://sigma5.blogspot.com/2010/11/space-shuttle-rip.html. Here's a link to my most recent post: http://sigma5.blogspot.com/2015/11/rocket-science-in-fact-and-fiction.html. It turns out that I tend to repeat myself. The reason is that when it comes to the economics of rocket ships nothing changes. Clarke hits the highlights in "Exploration". His observations were based on the state of the art in the '50s. Not much has changed.
My 90-9-1 formula is still pretty much unchanged. A rocket consists of 90% fuel, 9% structure, and 1% payload. And it costs about $10,000 per pound to put a payload into LEO. That's pretty much what Clarke said. That's what I have said on several occasions. In one of my posts I noted that Elon Musk said he could get it down to $5,000 per pound. So as I was writing this I went on the Internet and got some numbers for the SpaceX Falcon 9, Musk's rocket. Fueled up and ready to go, the latest version ("full thrust") weighs 1,210,457 lbs. on the launch pad. The list price for a launch is $62 million.
So how many pounds can it put into LEO? Well, there are three answers. The first one is 50,265 lbs. That would mean that 4% of the rocket is payload. That sounds like a big improvement. But the devil is in the details. A Falcon 9 is a three stage rocket. It has a large main stage and a relatively small second stage. Then there's what you put on the top of the second stage. This includes but is not limited to the payload. The total weight of whatever you put on top of the second stage can weigh up to 50,265 lbs. and it will make it to LEO. And it would be great if it was all payload. But it isn't.
If you want to buy the whole package from SpaceX then you need a PAF (Payload Attach Fitting). SpaceX gives you two options. A "heavy" PAF will accommodate 24,000 lbs. of payload. This means that the payload now constitutes 2% of the total weight. And this pencils out to roughly the $5,000/lb. Musk promised. So we're all good now, right. Not completely. SpaceX also offers a "light" PAF. If you go with the light PAF you are limited to a payload of 7,612 lbs. Now we are back to about $10,000/lb.
It is broadly reported that SpaceX missions to the ISS deliver about 5,000 lbs. of material. Given the press's propensity for simplification and approximation I'm going to assume that the PAF used to deliver supplies to the ISS is the light one. For things to work the payload must be able to navigate, change orbit, and rendezvous with the ISS. This takes a complex package with fuel, rockets, and other stuff. It include all this capability requires that the PAF be heavier so the size and weight of the actual payload must be smaller and lighter.
This is a classic example an old saw I invented that says "the bullet items giveth and the fine print taketh away". If you want to provide your own PAF then a Falcon 9 will be able to deliver a total package weighing about 50,000 lbs. to LEO. If your needs are simple (just something to protect your satellite during launch and give it a small kick into your preferred orbit) then a heavy PAF will work for you and your payload can weigh as much as 24,000 lbs. But if you need a "full function" PAF, something that can deliver your payload to the ISS, for instance, then you need the light PAF and your payload must weigh no more than 7,612 lbs.
So are we really doing better? Before they added safety improvements the old Space Shuttle could deliver itself, several astronauts, a life support environment and supplies for said same astronauts, a handy extension arm, and 62,000 lbs. of payload to the ISS. And it could do it for roughly $10,000/lb.
It is early days for SpaceX and the Falcon 9. It has rapidly evolved through several versions in a few years. Once the research and development costs are recovered and the design and construction stabilizes it is hoped by everybody that the per launch cost of a Falcon 9 will go down quite a bit. But even if SpaceX can deliver supplies to the ISS for $5,000/lb. access to space will continue to be fantastically expensive.
And that means that a lot of things, a return of astronauts to the moon as anything other than a publicity stunt, sending people to Mars and returning them safely, mining asteroids, anything that requires sending a lot of material to space, is just going to be too expensive to pay its own way. Today weather satellites and communications satellites pay their own way. Scientists argue that certain exploratory missions pay their own way and I agree with them. But lots of people disagree with that position.
So until there is a breakthrough that neither Arthur C. Clarke nor I can foresee happens that drastically reduces the cost of access to LEO very few "space" projects are going to get funded. And that means that for the foreseeable future (always a chancy proposition) people flying all over the place in space ships will continue to exist only in realms of Science Fiction. That has been distressingly true for far too long a time. Unfortunately, the chances of a breakthrough that would change things is and continues to be vanishingly small.
No comments:
Post a Comment